Reduction of aromatic nitrogen compounds



Patented July 14, 1953 REDUCTION OF AROMATIC NITROGEN COMPOUNDS Allen Walter Sogn, Buffalo, N. Y., assignor to Allied Chemical & Dye Corporation, New York, N. Y., a corporation of New York No Drawing. Application September 9, 1950, Serial No. 184,123

23 Claims. 1

This invention relates to improvements in the alkaline reduction of aromatic nitrogen compounds containing nitrogen in a reducible form as a nuclear substituent. It relates more particularly to improvements in the process of effecting the reduction, by means of alkaline reducing agents, of such aromatic nitrogen compounds, and especially mononuclear aromatic nitrogen compounds of said type, in which the nitrogen is at a higher stage of oxidation than the hydraeo stage.

The alkaline reduction of aromatic nitrogen compounds containing nitrogen in a reducible form is well known. Thus it is known to reduce aromatic nitro compounds, aromatic nitroso compounds, aromatic azoxy compounds, aromatic azo compounds and aromatic hydroxylarnino compounds by means of alkaline reducing agents. It is also known that the extent to which the reduction can be carried depends on the strength of the reducing agent and the severity of the reduction conditions.

For example, it is known to reduce nitrobenzone with a metal alcoholate, and especially an alkali metal alcoholate. The reduction is usually carried out by heating nitrobenzene with alcoholic caustic alkali (e. g., sodium hydroxide and an alcohol) at the boiling point of the mixture while refluxing at atmospheric pressure. Alkali metal hydroxide and an alcohol are used instead of the equivalent preformed alcoholate because of lower cost. Methanol is preferred as the alcohol in view of its relative cheapness. The reduction product, a side from a small amont of aniline, is azoxybenzene; the alkali metal alcoholates are not sufliciently strong reducing agents to carry the reduction beyond the azoxy stage, under the usual conditions.

Heretofore, it has been necessary to carry out the further reduction of azoxybenzene to azobenzene, and of azobenzene to hydrazobenzene, with stronger reducing agents, such as zinc and alkali, which are more costly than the alcoholic caustic alkali reducing agents.

It has been proposed to carry the reduction of nitrobenzene beyond the azoxy stage by heating it with sodium or potassium hydroxide and methanol under more elevated temperatures and pressures, such as temperatures of 140 to 180 C. and pressures of or more atmospheres. Such a procedure has the usual disadvantages of operation under pressure, as well as requiring expensive pressure apparatus.

lhus, the production of aromatic azo and hydrazo compounds from aromatic nitro compounds and their intermediate reduction products pre- 2 sents a number of problems from the standpoint of commercial practice.

A primary object of the present invention is to provide improvements in the alkaline reduction of reducible aromatic nitrogen compounds of the type referred to above (1. e., containing nitrogen in a reducible form as a nuclear substituent), whereby the reducing power of metal alcoholate reducing agents and especially of alcoholic caustic alkali reducing agents is enhanced and other advantages are secured.

Other objects of the present invention are to provide a process for the production of aromatic azo compounds in excellent yields by the reduction of aromatic nitro compounds, and their reduction products up to and including azoxy compounds, with metal alcoholates under moderate reaction conditions and in simple apparatus; to provide a process for the production of aromatic hydrazo compounds by reduction of aromatic nitro compounds and other reducible aromatic nitrogen compounds with metal alcoholates under moderate conditions and in simple apparatus; and to provide improvements in the reduction of reducible aromatic nitrogen compounds with metal alcoholates whereby the evolution of hydrogen gas during the reduction is suppressed.

Additional objects in part will be obvious and in part will appear hereinafter.

According to the present invention, the foregoing objects are accomplished by carrying out the reduction of reducible aromatic nitrogen compounds by means of a metal alcoholate with the inclusion in the reaction mixture of a reduction promoter of a novel class.

The novel class of reduction promoters employed in accordance with the present invention, which class is designated herein by the expression naphthoquinoid compounds, consists of the various naphthoquinones (whether free from nuclear substituents besides the quinone oxygen atoms or containing additional nuclear substituents wherein one or more of the hydrogen atoms of the naphthoquinone nucleus are substituted by another atom or radical; as for example, halogen, hydroxyl, nitro, mercapto, amino, cyano, sulfo, carboxy, alkyl, alkoxy, etc.) addition compounds of such naphthoquinones (such as addition compounds of the naphthoquinones with inorganic or organic bisulfites or with heavy metal salts), functional derivatives of such naphthoquinones (such as, imides, oximes, semicarbazones, hydrazones, etc., obtainable by condensation of the naphthoquinones with various ammonia derivatives), and the various tautomeric forms of desures of or more atmospheres.

rivatives which are capable of isomerizing to such naphthoquinones.

Thus, said class of naphthoquinoid compounds includes:

1,4-naphthoquir1one 1,2-naphthoquinone 2,6-naphthoquinone 2,3-dichloro-lA-naphthoquinone Z-hydroxy-IA-naphthoquinone 2-methyl-1, l-napthoquinone Z-nitro-lA-naphthoquinone l chloro 6 bromo l methyl 2,3 naphthoquinone 5,8-dihydroxy-1,4-naphthoquinone 1,4 naphthoquinone oxime or 4 nitroso 1- naphthol 1,2 naphthoquinone oxime or 1 nitroso 2- naphthol 2-methylamino-lA-naphthoquinone 2-monoethy1amino-1,4-naphthoquinone 2-diethanolamino-1,4-naphthoquinone 2-ani1ino-lA-naphthoquinone l,2 naphthoquinone-4-sulfonic acid 1, naphthoquinone-iz-sulfonic acid 1 i-naphthoquinhydrone lA-naphthoquinone dioxime 1,2-naphthoo,uinone dioxime 1,4-naphthoquinone monoformylhydrazine l A-naphthoquinone monosemicarbazone lA-naphthoquinone bis oxime acetate 1,4-naphthoquinonanil 1, l-naphthoquinonedianil lA-naphthoquinonimide anil N (p dimethylaminophenyl) 1,4 naphthsquinonimine Addition products of naphthoquinones with inorganic bisulfites (such as, those with sodium,

ample, as disclosedin U. S. P. 2,367,302)

Addition products of naphthoquinones with heavy metal salts (such as, those with tin chloride and antimony chloride, which can be prepared, for example, as disclosed in Berichte, vol.

41, page 2573).

I have discovered that the presence in the reaction mixture of a small amount of a naphthoquinoid compound, such as 1,4-naphthoquinone, has a modifying efiect upon the reduction, as a result of which a number of benefits may be secured.

Thus, as compared with a reduction carried out under the same conditions but in the absence of the naphthoquinoid compound, the speed of the reduction is increased and/or products of a higher stage of reduction are obtained, without substantial sacrifice of the total yield of'reduction products secured from the starting material. In the reduction of aromatic nitro compounds, the presence of a naphthoquinoid compound in the metal alcoholate reaction mixture makes possible the obtainment of azo compounds directly, Without requiring the use of drastic operating conditions, such as high temperatures and pres- Siinilarly, the presence of a naphthoquinoid compound in the medium makes possible the use of milder reaction conditions or the use of decreased amounts of reducing agent. Thus, in the reduction of an aromatic nitro compound with. sodium hydroxide and methyl alcohol, the presence of a naphthoquinoid compound in the reaction mixture makes possible the use of a lesser amount of sodium hydroxide, thereby decreasing the cost of the operation.

In the case of the reduction of ortho-nitrotoluene, the presence of the naphthoquinoid compound exerts an additional beneficial efiect, since it results in the obtainment of a total yield of azotoluene and azoxytoluene which is considerably greater than the yield of azoxytoluene obtained under the same conditions in the absence of the .naphthoquinoid compound.

Or" the naphthoquinoid compounds, those which are 1,2- and lA-naphthoquinones or addition compounds or derivatives thereof are preferred for use in the reduction of reducible aromatic nitrogen compounds by means of metal a1- coholates. addition products and 2,3-dichloro-L4-napthoquinone are especially preferred in view of their outstanding activity as reduction promoters coupled with their availability and relatively low cost.

In the practice of the present invention, the reducible aromatic nitrogencompound is subjected to the reducing action of a metal alcoholate reducing agent in a reaction mixture containing one or more naphthoquinoid compounds as a reduction promoter. In the preferred practice of the invention, wherein a reducible aromatic nitrogen compound is heated with a caustic alkali and an alcohol (preferably sodium hydroxide and methanol) at the boiling point of the reaction mixture, the naphthoquinoid compound is preferably mixed with the alcohol and, after adding the caustic alkali and heating, the nitrogen compound to be reduced is added to the mixture.

The naphthoquinoid compound may be added to the reaction mixture in various Ways and at various times, however, Without departing from the scope of the invention. If desired, it can be preformed separately and added to the reaction mixture or it can be formed in the reaction mixture. Thus, when the naphthoquinoid compound is employed in the form of an addition product of a naphthoquinone with a bisulfite or a heavy metal salt, the addition compound can be formed in the alcohol employed as a part of the reaction mixture prior to the addition of the other reactants.

The naphthoquinoid compound can be employed in various amounts. It is a feature of the present invention that only small amounts of the naphthoquinoid compounds are required. Thus, in the specific examples set out below, amounts ranging from ,5, to 1 mol of naphthoquinoid lA-naphthoquinone and its bisulfite d compound per mol of reducible aromatic nitrogen compound are employed. The minimum amount required to produce a significant reduction-promoting effect varies with the individual naphthoquinoid compound, the'nature of the reducible aromatic nitrogen compound, and the reaction conditions. In general, a greater reduction-promoting effect is secured by increasing the amount of naphthoquinoid compound employed and a lesser eifect results from decreasing the amount employed, other reaction conditions being constant. Ordinarily, amounts greater than about mol of naphthoquino'id compound per mol of reducible aromatic nitrogen compound are not advantageous, although 1 they may be used if desired, since the increased cost of the extra naphthoquinoid compound is not sufficiently compensated by the additional benefits derived therefrom to be of commercial Example 1 Part A.360 parts of methanol and 4.8 parts of 1,4-naphthoquinone were charged to a flask equipped with a reflux condenser, agitator, dropping funnel and thermometer. 4.46 parts of soild sodium hydroxide were then added over the course of minutes. The mixture was heated to refluxing, 738 parts of nitrobenzene were added, and the reaction mass was boiled and refluxed (about 90 to 105) for hours under atmospheric pressure. A negligible amount of gas was evolved during the addition of nitrobenzene nad subsequent reflux period. Unreacted methanol was then removed by distillation with live steam, after which the mass was allowed to stand and separate into an upper oil phase and a lower aqueous phase. The aqueous phase, consisting essentially of sodium hydroxide and sodium for-' mate in solution, was drawn off at about l00 and the oil phase was clarified by filtration from a small amount of blank insoluble residue. The resulting oil, which contained less than 1% of moisture partially emulsified therein, consisted essentially of azobenzene. After being dried over calcium chloride, it had a setting point of 65.6". The yield was 535 parts, which corresponds to to about 98% of the theoretical yield of azoben- Zene, based on the nitrobenzene charged.

Part B.-The process of Part A was repeated without addition of the lA-naphthoquinone. 25,000 parts by volume of hydrogen were elvolved and the oil product, which amounted to 573 parts, consisted essentially of azoxybenzene (it had a setting point of 335). This corresponds with a yield of about 96% of the theoretical yield of azoxybenzene.

Example 2 The procedure described in Example 1, Part A, was repeated, using parts of a crude 1,4- naphthoquinone-containing product identified as phthalic anhydride scale in place of the 1 1- naphthoquinone. The phthalic anhydride sca1e Was obtained in the manufacture of the theoretical,

6 phthalic anhydride by catalytic air oxidation of naphthalene vapors, wherein the gaseous oxidation products were passed into customary atmospherically-cooled box condensers to condense phthalic anhydride. Most of the product obtained condenses within such condensers as socalled needles and hay, which are relatively pure forms of phthalic anhydride; some of the product condenses on the walls as a scaly deposit known as scale, which is a relatively impure form of phthalic anhydride containing a substantial amount of naphthoquinone. The product weighed 534 parts and consisted essentially of azobenzene (setting point of 66.1"). This corresponds with a yield of about 98% of the theoretical, based on the nitrobenzene charged.

Example 3 The procedure described in Example 1, Part A, was repeated, using 5 parts of 2,3-dichloro- IA-naphthoquinone in place of the lA-naphthoquinone. The product weighed 505 parts and consisted of azobenzene (setting point of 681). This corresponds with a yield of about 92.5% of based on the nitrobenzene charged. In addition 35 parts hydrazobenzene were obtained.

Example 4 360 parts of methanol, 6 parts of technical 1,4-naphthoquinone, and 10 parts of sodium metabisulfite (NazSzOs) were refluxed for a few hours to form a 1, l-naphthaquinone-sodium bisulfite addition product. Then 446 parts of sodium hydroxide were introduced and, while boiling the mixture, 738 parts of nitrobenzene were added. The mixture was boiled and refluxed for about 20 hours under atmospheric pressure. The unreacted methanol was removed by steam distillation, and the residue was allowed to stand and separate into two phases. The upper layer of oil was separated from the lower dark, aqueous sodium hydroxide-sodium formats layer, and filtered to remove a small amount of dark colored residue. (When dry this residue amounted to about 0.3 part, or less than one-tenth the amount, otbained when the bisulfite was omitted, as in Example 1, Part A, above.) The oil thus obtained (542 parts) was slurried with 1l6 parts of Be. hydrochloric acid dissolved in 1000 parts of water at about 100, and the mass was cooled to about room temperature and filtered. The product, after being dried, had a setting point of 67.9", which corresponds to substantially pure azobenzene. The yield was 473 parts. The filtrate from the acid wash, when titrated with standard sodium nitrite, was found to contain an amount of benzidine corresponding to about 65 parts of hydrazobenzene.

By the use of the reduction promoter prepared from sodium metabisulfite and 1,4-naphthoquinone in the substantial absence of water, it was possible to secure the high reduction-promoting efiiciency of lA-napthoquinone while forming so little dark colored residue as to render its removal practically unnecessary.

Example 5 The procedure described in Example 1, Part A, was repeated using, in place of the 1,4-naphtho quinone, 7.8 parts of the crystalline sodium bisulfite addition product of lA-naphthoquinone produced by the method described in United States Patent 2,331,808 from 1.58 parts of 1,4- naphthoquinone and 0.95 part of sodium metabi- Potassium bisulfite addition product of 1,4- naphthoquinone, produced by the process of U. S. P. 2,331,808 from 1.58 parts of 1,4-naphthoquinone and 1.11 parts of potassium metabisulfite (K2S2O5).

Example 7 Sodium bisulfite addition product of ,2-methyl- 1,4-naphthoqt1inone, produced as described in U. S. P. 2,331,808 from 1.72 parts of .2-methyl- 1,4-naphthoquinone and 1.04 parts of sodium bisulfite (NaHSOs).

Example 8 Addition product of potassium bisulfite and 2-methyl-1,4naphthoquinone, produced by the method of U. S. P. 2,331,808 from 1.72 parts of the quinone and 1.11 parts of potassium metabisulfite (KzSzOs).

Example 9 Tin chloride addition product of 1,4-naphthoquinone, produced by reacting the quinone with stannic chloride (SnCh) as described in Berichte 64 (1931) pp. 1660 and 1663.

Example 10 Antimony pentachloride addition product of 1,4-naphthoquinone, produced by reacting the quinone with antimony pentachloride (SbCls) as described .in Berichte 41 (1908) p. 2573.

Example 11 Antimony pentachloride addition product of 2-methy11,4-naphthoquinone, produced by reacting the quinone with antimony pentachloride according to the general procedure described in Berichte 64 (1931) p. 1660.

Example '12 Antimony pentachloride addition product of 2,3-dichloro-.1,4-naphthoquinone, produced by reacting the quinone withantimony pentachlorideaccording to the generalprocedure described in Berichte 64 (1931) p. .1660.

Aside from a reflux period of .24 hours in the case of Examples 6 and 10, the conditions were thelsame as in Example 1, PartA. The yield and composition. of theproduct thus obtained are set forth inthe following table.

TAB-LE Product Weight of Example Addition b etting Percent Percent Num 91 Product welgghtt Point Azoxy Amy ar 5 in C. benzene benzene Example 13 360 parts of methanol, 6parts of 1,4-naphthoquinone and 6 parts of monomethylamine acetate were charged to a flask and stirred at about 30 for a half hour to form 2-methylamino-1,4- naphthoquinone. 446 parts of caustic soda were added, the mixture was heated to refluxing, and then'738 parts of nitrobenzene were introduced. The reduction and subsequent processing were carried out as described in Example 1, Part A. The product weighed 516 parts and consisted essentially of azobenzene (it had a setting po'mt of 66.3") This corresponds with a yield of about of the theoretical, based on the nitrobenzene charged.

I Example 14 The procedure of Example 13 was carried out with substitution of the 2-methylamino-1,4- naphthoquinone by 2-anilino-1,4-naphthoquinone, which was prepared by charging 360 parts of methanol, 6 parts of 1,4-naphthoquinone and 12 parts of aniline to the flask and stirring at about 30 for one-half hour. The results obtained were similar to those of Example 13.

Example 15 Similarly, the 2-methylamino-l,4-naphthoquinone employed in Example 13 was replaced by Z-diethanolamino-1,4-napthoquinone, which was prepared by charging 360 parts of methanol, 6 parts of 1,4-naphthoquinone and 6 parts of diethanolamine to the flask and stirring at about 30 for one-half hour. The results obtained were similar to those of Example 13.

Example 17 The procedure described in Example 1, Part A, was repeated with 6 parts of 2-hydroxy-1,4- naphthoquinone in place of the 1,4-naphthoquinone. The product weighed 528 parts and consisted essentially of about 62.5% of azobenzene and 37.5% of azoxybenzene (it had a setting point of 49.8).

' Ezrample 18 The procedure described in Example 1, Part A, was repeated with 6 parts of 1,4-naphthoquinone-2-sulfonic acid in place of the 1,4-naphthoquinone. The product weighed 540 parts and consisted essentially of about 61% of azobenzene and 39% of azoxybenzene (it had a setting point of 49).

Example 19 The procedure described in Example 1, Part A, was repeated with 12 parts of 1,2-naphthoquinone in place of the 1,4-naphthoquinon6. The product weighed 528 parts and consisted essentially of about 63% azobenzene and 37% azoxybenzene (it'had'a setting point of 50.2").

Example 20 Part A.--360 parts of methanol and 4.8 parts of 1,4-naphthoquinone were charged to a flask equipped with a reflux condenser, agitator,

about 55% azobenzene and 45% azoxybenzene' (it had a setting point of 45.2). This corresponds, respectively, to 55% and 41% of the theoretical yields of azobenzene and azoxybenzene, or 96% of the theoretical yield of combined azoand azoxybenzenes, based on the nitrobenzene charged.

Part B.--The process of Part A was repeated without addition of the lA-naphthoquinone.

Hydrogen in the amount of 22,600 parts by volume was evolved, and the product, which amounted to 574. parts,-consisted essentially of azoxybenzene (it had a setting point of 33.6).

Example 21 The black, insoluble residue removedin the clarification of the oil product obtained in Example 1, Part A, and which is presumed to be a polymerization or condensation product derived from 1,4-naphthoquinone, was employed as reduction promoter by replacing the lA-naphthoquinone in the process of Example 1, Part A, by

12 parts of the insoluble black residue. The

product weighed 543 parts and consisted essentially of about 46% azobenzene and 54% azoxybenzene (it had a setting point of 383).

Example 22 360 parts of methanol, 550 parts of sodium hydroxide, 27 parts of IA-naphthoquinone, and 738 parts of nitrobenzene were charged to a flask of the type employed in Example 1. The mixture was refluxed 42 hours under atmospheric pressure. The methanol was steam distilled and the aqueous distillation residue was poured into 2000 parts of cold water. The aqueous liquor was decanted from the hydrazobenzene crystals, and. the crystals were washed with about 5000 parts of water in separate washes. The wet hydrazobenzene crystals were comminuted to particles of about 100 mesh size. The resulting paste of hydrazobenzene was directly converted to benzidine by slurrying it in 500 parts of water, adding 290 parts of 20 Be. hydrochloric acid at to agitating the mixture 4 hours at 10 to 15, then adding 343 parts of 50 B. sulfuric acid in 8 hours at 10, allowing the temperature to rise to 30 and agitating the mixture at about 30 for 10 hours. for 2 hours to complete the rearrangement reaction, after which 450 parts of sodium sulfate were added to promote precipitation of the benzidine sulfate, which was then separated as a cake by filtration, and washed acid free to Congo with water.

The benzidine sulfate paste thus obtained weighed 1598 parts and contained 451 parts of benzidine, which corresponds to 82% of the theoretical yield of benzidine from nitrobenzene. 7

By carrying out the reduction reaction at a little higher temperature under slightly'superatmospheric pressure (e. g., 10 to pj-s. i.) a simi1ar result can be obtained in a shorter reaction period. r

The mixture was then heated to 70 10 Example 23 Part A.--360 parts of methanol and 4.8 parts of 1,4-naphthoquinone were charged to a flask of the type employed in Example 1, and 446 parts of solid sodium hydroxide were added slowly portionwise. The mixture was heated to refluxing, 822 parts of ortho-nitrotoluene were introduced slowly while continuing refluxing, and the mixture was boiled and refluxed thereafter for about 20 hours with vigorous agitation. Unreacted methanol was then distilled with live steam, whereupon the mass Was allowed to settle and-the lower aqueous phase was drawn ofi. The oil layer was clarified by filtration from a small amount of insoluble residue noted previously, and the clarified oil was washed free from orthotoluidine with 2000 parts of hot water containing suflicient hydrochloric acid to maintain acidity to Congo. The washed oil thus obtained, after being dried over calcium chloride, had a setting point. of 51.8. The product weighed 572 parts and consisted essentially of a mixture of 412 parts of o,o-azoxytoluene and 160 parts of 0,0'-azotoluene. This yield corresponds to 86.1% of the theoretical yield of combined azoxytoluene and azotoluene.

Part B.--The process of Part A was repeated without the addition of the 1.4-naphthoquinone. Hydrogen in the amount of 31,000 parts by volume was evolved, and the product consisted essentially of o,o'-azoxy toluene (it had a setting point of 545 and did not possess the characteristic red color of azotoluene). The product weighed 457 parts, which corresponds with a yield of about 67% of the theoretical yield of o,oazoxytoluene based on the nitrotoluene charged.

Example 24 Part A.360 parts of methanol, 500 parts of sodium hydroxide and 5 parts of 2,3-dichloro-L4- 'naphthaquinone were charged to a flask of the type employed in Example 1, and 918 parts of onitroanisole were introduced slowly at the boil. The mixture was boiled and refluxed for about 30 hours. Unreacted methanol was then distilled with live steam, and the residue was allowed to stratify. The oil layer was separated and freed from anisidine by agitating it with 3700 parts of about 5% aqueous hydrochloric acid at to cooling to cause graining of the oil, and filtering. The filter cake was washed acid free with water and dried. The

product weighed 431 parts and consisted essentially of a mixture of o-azoxyanisole and. o-azoanisole (it had a melting point of In addition, 28 parts of o-hydrazoanisole (identified dianisidine hydrochloride) and 221 parts of "o-anisidine which was also formed by the reduction, were present in the combined steam distillate and filtrates obtained above.

Part B.--The process of Part A was repeated without addition of 2,3-dichloro-1,4-naphthoquinone. The dried filter cake which consisted of o-azoxyanisole (setting point of 805) weighed 719 parts. This corresponds with a yield of about i 94% of the theoretical, based on the o-nitroanisole charged. In addition, 25 parts of oanisidine, corresponding to about 3% of the theoretical yield of o-anisidine, were present in the combined steam distillate and washflltrates.

Example 25 was complete (about 45 hours). was then removed by distillation with live steam were refluxed together at atmospheric pressure until reduction to the colorless hydrazotoluene The methanol (the steam distillate contained about 60 parts of o-toluidine) the aqueous residue was filtered, and the filter cake of o-hydrazotoluene was washed alkali free with water. of o-hydrazotoluene was directly converted to o-tolidine by slurrying in 7000 parts of water, adding 1160 parts of 20 B. hydrochloric acid at to agitating the mixture at 15 to f.or about 20 hours, then adding 5 parts of zinc and 6'75 parts of 50 B. sulfuric acid, and agitating the mixture at 20 to for about 20 hours. After warming to 10, 5 parts of zinc and 750 parts of Be. sulfuric acid were introduced to promote precipitation of o-tolidine sulfate, the resulting precipitate was filtered off at about 70, and the cake was washed acid free with cold water. The resulting product contained 420 parts of o-tolidine, based on analysis of the sulfate. The mother liquors contained an additional amount of o-tolidine sulfate equivalent to 19 parts of o-tolidine.

Example 26 Part A.360 parts of methanol, 5 parts of 2,3- dichloro-l,4-naphthoquinone and 220 parts of sodium hydroxide were charged to a flask of the type referred to above, 546 parts of azobenzene (setting point of 65) were added, and the mixture was boiled with refluxing (temperature of 98 to 100) at atmospheric pressure for a period of about 20 hours. At the end of this time, the red azobenzene had been completely replaced by substantially white crystals of hydrazobenzene. The reaction mixture was diluted with 270 parts of methanol, cooled to 30, and filtered by pouring it onto a 40 mesh screen. The filter cake was washed three times by slurrying it in methanol and filtering the slurry, using 270 parts of methanol per wash. The washed cake was reslurried in water, and the methanol was removed by steam distillation. The residue was cooled, filtered at about room temperature, and the filter cake was washed alkali free and dried. The 7 product consisted essentially of hydrazobenzene (it had a setting point of 125.2). It weighed 485 parts, which corresponds with a yeild of about 88% of the theoretical yield of hydrazobenzene, based on the azobenzene charged.

Part B.-Substantially no reduction of the azobenzene to hydrazobenzene was effected (over 99% of the azobenzene was recovered) when the the process of Part A was repeated without the addition of 2,3-dichloro-1,4-naphthoquinone, even when the amounts of methanol and sodium hydroxide were increased to 425 parts and 445 parts, respectively, and the refluxing period was extended to about 30 hours.

7 Example 2.7

The filtrates and wash liquors obtained in Example 26, Part A, were combined, yielding a solution containing approximately 140 parts of sodium hydroxide, 1100 parts of methanol, 65 parts of hydrazobenzene, and an unknown amount of 2,3-dichloro-1,4-naphthoquinone or transformation product thereof. The solution was fortified with 80 parts of sodium hydroxide and 1 part of 2,3-di-chloro1,4-naphthoquinone, and 546 parts "of azobenzene were added. The mixture was The resulting filter cake heated to boiling (about and boiling was continued for about 4 hours, 740 parts of meth anol being distilled off and recovered and the temperature rising to about The mixture was then boiled andrefiuxed for about 18 hours, at the end of which time the red azobenzene had been replaced by substantially white crystals of hydrazobenzene. The reaction mass, when worked up in the manner described in Example 26, yielded 530 parts of hydrazobenzene.

EmampZe 28 Part A.360 parts of methanol, 4.8 parts of 1,4-naphthoquinone and 446 parts of sodium hydroxide were charged to a flask of the type referred to above. 467 parts of a mixture consisting essentially of 72% azobenzene and 28% azoxybenzene (having a setting point of 556) were introduced into the refluxing mixture, and the reaction mass was then refluxed for 17 hours. Unreacted methanol was removed by steam distillation, and the residue was allowed to stand and separate into an upper oil layer and a lower aqueous layer. The latter was withdrawn, and the oil which contained hydrazobenzene and unreduced azobenzene, was diluted with benzene and decanted from an emulsion layer which formed. The benzene solution of the oil was mixed with 290 parts of 50 B. sulfuric acid at 25 to 30, and the mixture was heated to 65, at which temperature the benzene phase was decanted from the gray paste of benzidine sulfate Which formed. The paste was slurried in water, residual benzene Was removed by steam distillation, and the mass was filtered at room temperature. The moist filter .cake amounted to 238 parts and contained 128 parts of benzidine as the sulfate.- The filtrate from the benzidine sulfate contained 18.6 parts of diphenylines. The total yield of'benzidine and diphenylines is equivalent to a yield of 146.6 parts of hydrazobenzene in the reduction product. The decanted benzene solution, on evaporation to dryness, left a residue weighing 285 parts and consisting essentially of azobenzene (it had a setting point of 6'7.'7).

Part B.No reduction of azoxybenzene was effected (over 99% of the azoxy-benzene was recovered) when it Was heated with'methanol and caustic soda in the manner of Part A, but in the absence of 1,4-napht'hoquinone. The presence of the 1,4-naphthoquinone in the process of Part A resulted in the reduction of all of the azo-xybenzene and a part of the azobenzene.

Example 29 546 parts of azobenzene, 100 parts of methanol, 100 parts of sodium hydroxide, 5 parts of 2,3- dichloro-l,4-naphthoquinone and 260 parts of xylene were refluxed under atmospheric pressure (maximum temperature of 97), and the course of the reduction was checked at intervals. Reduction to hydrazobenzene was 30% complete in 18 hours, 50% complete in 66 hours, and substantially complete in 144 hours. The resulting mixture was diluted with 300 parts of water, and the xylene was removed by steam distillation at constant volume. The resulting ,mass was filtered and the filter cake of hydrazobenzene was washed alkali free and dried. The

product weighed 545 parts and consisted of hydrazobenzene (it had a setting point of 123). This corresponds with approximately 99% of the theoretical yield-of hydrazobenzene, based on the azobenzene charged.

Example 30 360 parts of methanol, 15 parts of 1,4-naphthoquinone and 15 parts of sodium metabisulfite were charged to a flask of the type employed in Example 1. The mixture was refluxed under atmospheric pressure for one hour, whereupon it was cooled to 30 and 500 parts of sodium hydroxide were added with cooling. After heating the flask contents to boiling, 822 parts of o-nitrotoluene were introduced during about two hours into the boiling mixture, which was further refluxed and boiled for 17 hours under atmospheric pressure. During the addition of o-nitrotoluene and subsequent refluxing, the reaction mixture was agitated vigorously and its temperature ranged from 92 to 105. The reaction mixture was cooled to 60 and 980 parts of methanol and 250 parts of sodium hydroxide were added. The mixture was then heated to boiling and refluxed under atmospheric pressure for 24 hours (temperature 88). Thereafter, 635 parts of methanol were removed by distillation during 4 hours to raise the reflux temperature to 98, and the resulting reaction mixture was As noted above, the invention is not limited to r the details of the foregoing illustrative examples, and changes can be made without departing from the scope of the invention.

Thus, the process is applicable to the reduction of other aromatic nitrogen compounds containing nitrogen in a reducible form as a nuclear substituent, as for example, m-nitrotoluenc, o nitrochlorobenzene, m nitrochlorobenzene, o-nitrophenetole, o-nitrobenzoic acid and o-nitrobenzene sulfonic acid. In view of the extensive use of hydrazobenzene and its o-substituted derivatives (such a 0,0-dichloro-hydrazobenzene, o,o'-hydrazotoluene', o,o-hydrazoanisole, o,o'-diethoxy-hydrazobenzene, etc.) as intermediates for thev manufacture of benzidine and related derivatives of benzidine, the process of the present invention is of special value as a means for reducing the cost of manufacturing such hydrazo compounds from the corresponding reducible mononuclear aromatic nitrogen compounds (such as, nitrobenzene and its o-substituted derivatives and reduction products thereof) in which the nitrogen is at a higher stage of oxidation than the hydrazo stage.

The reduction of aromatic nitro compounds to azoxy compounds 1, of azoxy compounds to azo compounds 2, and of azo compounds to hydrazo compounds 3 proceeds accordingto the following equations, in which R is an aromatic nucl us:

In carrying out the reduction by means of sodium hydroxide and methanol, it is preferable to employ these reagents in amounts in excess of those theoretically required. Extra methanol over that theoretically required is generally desirable for use as a solvent, and an additional excess is desirable to counteract the diluting effect of the water generated in accordance with above Equations 1 and 2, which would otherwise tend to retard the reaction. An excess of sodium hydroxide also is desirable since it tends to increase the rate of reaction.

As is evident from the examples, it is possible to carry the reduction of a particular reducible aromatic nitrogen compound to various stages, depending upon the amounts of sodium hydroxide and methanol, as well as the nature and amount of naphthoquinoid compound, employed. Thus, it is possible to reduce nitrobenzene to hydrazoj benzene in a single reaction mixture, as illustrated in Example 22. However, it is possible to reduce nitrobenzene to azoxyand/or azobenzenein one reaction mixture as illustrated in Example 1, and then to isolate and reduce the resulting azoxybenzene and/or azobenzene to hydrazobenzene with a fresh charge of sodium hydroxide and methanol, as illustratedin Examples 26 to 29.

The temperature at which the reaction is carried out also may be varied although, in the reduction performed with the aid of alcoholic caustic alkali, temperatures at or near the boiling point of the reaction mixture at atmospheric pressure (ordinarily about to are preferred. At lower temperatures, the reaction is slower, under otherwise similar conditions, and may require an excessively 10l'1g time to produce the same results as the preferred temperatures. Conversely, higher reaction temperatures result in a short time cycle but require the use of closed reaction vessels. However, temperatures greatly exceeding though not precluded, are less desirable; since even in the presence of the naphthoquinoid promoters they lead to evolution of considerable amounts of hydrogen gas and formation of primary amines, with consequent loss of yield of the desired reduction products.

While for economical and simple operation it is preferred to use, a a solvent or diluent of the reaction mixture, an excess of the alcohol employed for the alcoholate, the invention is not limited thereto. Thus, other solvents and diluents can be employed, as'illustrated in Example 29, wherein the process is carried out with amount of sodium hydroxide and methanol only slightly in excess over the amounts theoretically required for the reduction, in a reaction medium containing a sufficient amount of xylene to provide a stirrable reaction mass. Instead of xylene, other inert solvents or diluents may be used, such as benzene, toluene, monoand dichlorobenzenes. Further, while it is simpler to employ, as the solvent or diluent, an excess of the alcohol functioning as a reducing agent, other alcohols can be em loyed: also mixtures of alcohols can be used, especially where it is desired to modify the boiling temperature of the reaction mixture.

As a matter of convenience and for economical operation, the process is generally carried out by forming a metal alcoholate in the reaction mixture: for exam le, by reacting caustic alkali with t e alcohol. If desired, however. preformed metal alcoholates may be employed as reducing agents,

alkalis. (for example, potassium hydroxide) and other alcohols (for example, ethyl alcohol and the various propyl, butyl and higher alcohols) may be employed, if desired.

The products of the. reduction can be isolated from the reaction. mixtures in any suitablemanner. Aside from those cases, in which an insoluble residue is formed as a result of the presence. of a naphthoquinoid compound in the reaction. mixture, the isolation of the reduction products. can. becarried out. in the usual. manner.

Thus, for example, the reaction mixture may be cooled to crystallize the reduction product and filtered, and the cake washed with water to. remove alcohol,..scdium formate formed as a byproduct of the reduction, and sodium hydroxide. Generally, it is preferred to steam distill the ethanol (and. dehydrate the aqueou methanol thus obtained by fractional distillation for reuse in subsequent reactions) and then cool the remaining hot aqueous mass. to crystallize the reduction product, which may be washed as usual with water. Where. the product is molten in the hot mixture, as in the case ofazoxyand azocenzenes, it is simpler to stratify the mass into an. aqueous phase and an oil phase, whereupon the latter can be readil separated, as illustrated. inthe examples.

The naphtho uinoid compounds are generally soluble in the aqueous and/or alcoholic layer noted. above, and thus can be separated from the reduction product- When the use of a naphthoquinoid compound. produces a small amount of insoluble. lay-product, it may be removed. in any suitable manner, as. by filtering the hot mixture prior to the phase-separation, as illustrated in the examples.

I claim:

l. The improvement in the method of reducing an aromatic nitrogen compound containing nitrogen in a reducible form as a substituent in a benzene nucleus at a higher stage of oxidation than the hydrazo stage by the action of a metal alcoholate, which comprises ca 'rying out the reduction in a reaction mixture in which a naphthoquinoid compound has been incorporated, whereby the reduction of the aromatic. nitrogen compound is promoted. a.

2. A method as defined in claim 1. wherein the metal alcoholate is an alkali metal alcoholate and the nap-hthoquinoid compound is a naphthoquinone.

and the naphthoc uinoid compound is a naphthoquinone addition product.

a 5. A method as defined in claim 4 wherein the naphthoquinoid compound is a 1,lnaphthoquinone addition product.

6. A method of reducing an aromatic nitrogen compound containing nitrogen in a reducible form as a substituent in a benzene nucleus at a higher stage of oxidation than the hydrazo stage, which comprises heating the aromatic nitrogen compound with a reducing mixture of an alkali metal hydroxide and a lower alcohol in a reaction mixture in which a small amount of a naphthoquinoid compound has. been incorpo whereby the reduction of the aromatic nitrogen compound is promoted.

7. A method of reducing an aromatic nitrogen compound containing nitrogen in a reducible form as a substituent in a benzene nucleus at a higher stage of oxidation than the hydrazo stage, which comprises heating the aromatic nitrogen compound with a reducing mixture of sodium hydroxide and a lower alcohol in a reaction mixture containing a naphthoquinone in an amount corresponding with at least ,3 mol per mol of aromatic nitrogen compound, whereby the reduction of the aromatic nitrogen com pound is promoted.

8. A method of reducing an aromatic nitrogen compound containing nitrogen in a reducible form as a substituent in a benzene nucleus at a higher stage of oxidation than the hydrazo stage and selected from the group consisting of nitro benzene, an ortho-substituted nitrobencee, and reduction products thereof, which comprises heating the aromatic nitrogen compound with a reducing mixture of sodium hydroxide and a lower alcohol in a, reaction mixture in which a small amount of a naphthoquinoid compound has been incorporated, whereby the reduction of the aromatic nitrogen compound is promoted.

9. A method as defined in claim 8 wherein the naphthoquinoid compound in an amount correspending with at least mol permol or aromatic nitrogen compound is incorporated with. the reducing mixture and the aromatic nitrogen compound is heated with the residting reaction mixture.

It. A method as defined in claim 8- wherein a small amount of a 1,4-naphthoquinone is incorporated with methanol, sodium hydroxide is added, and the aromatic nitrogen compound is heated with the resulting reaction mixture.

11. A method as defined in claim 16 wherein the aromatic nitrogen compound is nitrohenzene and the naphtho uinone is selected from the group. consisting of 1,4-naphthoquinone and 2,3- dichloro-l/l-naphthoquinone.

12. A method as defined in claim 10 wherein the aromatic nitrogen compound is o-nitrotolnaphthoquinone addition product in an amount corresponding with at. least /soo mol per mol of aromatic nitrogen compound is incorporated with the reducing mixture and the aromatic nitrogen compound is heated with the resulting reaction mixture.

14. A method as defined in claim 13 wherein the naphthoquinone addition product is a bisulfite addition product of a naphthoquinone.

15. A method as defined in claim 14 wherein the naphthoquinone addition product is formed by reacting a bisulfite with a lA-naphthoquinone in a'lower alcohol, sodium hydroxide is added, and the aromatic nitrogen compound is heated with the resulting reaction mixture.

16. A method as defined in claim 13 wherein a lA-naphthoquinone addition product is incorby heating a 1,4-naphthoquinone with an alkali metal bisulfite in a lower alcohol.

18. A method as defined in claim 13 wherein the naphthoquinone addition product is formed by heating a 1,4-naphthoquinone with sodium bisulfite in methanol, sodium hydroxide is added, and nitrobenzene is heated with the resulting reaction mixture.

19. A method as defined in claim 13 wherein the naphthoquinone addition product is formed by heating a 1,4-naphthoquinone with sodium bisulfite in methanol, sodium hydroxide is added, and o-nitrotoluene is heated with the resulting reaction mixture.

20. A method as defined in claim 13 wherein the naphthoquinone addition product is a metal salt addition product of a 1,4-naphthoquinone.

21. A method as defined in claim 6 wherein the naphthoquinoid compound is a 1,4-naphthoquinoid compound.

22. A method of reducing an aromatic nitrogen compound containing nitrogen in a reducible form as a substituent in a benzene nucleus at a higher stage of oxidation than the hydrazo stage, which comprises reacting the aromatic nitrogen compound with an alkali metal methylate in a reaction mixture in which a naphthoquinoid compound has been incorporated, whereby the reduction of the aromatic nitrogen compound is promoted.

23. A method as defined in claim 6 wherein the naphthoquinoid compound in an amount corresponding with at least ,6 mol per mol of aromatic nitrogen compound is incorporated with a reducing mixture of sodium hydroxide and methanol and the aromatic nitrogen compound is reacted with the resulting reducing mixture.

ALLEN WALTER SOGN.

References Cited in the file of this patent UNITED STATES PATENTS Number 

1. THE IMPROVEMENT IN THE METHOD OF REDUCING AN AROMATIC NITROGEN COMPOUND CONTAINING NITROGEN IN A REDUCIBLE FORM AS A SUBSTITUENT IN A BENZENE NUCLEUS AT A HIGHER STAGE OF OXIDATION THAN THE HYDRAZO STAGE BY THE ACTION OF A METAL ALCOHOLATE, WHICH COMPRISES CARRYING OUT THE REDUCTION IN A REACTION MIXTURE IN WHICH A NAPHTHOQUINOID COMPOUND HAS BEEN INCORPORATED, WHEREBY THE REDUCTION OF THE AROMATIC NITROGEN COMPOUND IS PROMOTED. 